Plastic yielding of I-beams under shear, and shear and axial loading

Plane strain and plane stress slip-line field solutions previously published by the authors for cantilevers of rectangular cross-section are utilized to estimate the plastic collapse loads of corresponding I-sectioned beams. Uniform I-beams, tapered and haunched beams, and beams with rectangular holes and castellated beams are studied. Previous works in each case are reviewed and for uniform-section cantilevers with end shear loading, the results are compared with the theoretical results of others and with the experimental results of Green and Hundy.     

Low-energy electron-enhanced etching of HgCdTe

Low-energy electron-enhanced etching (LE4) is applied to HgCdTe to eliminate ion-induced surface damage. First, LE4 results for patterned samples are illustrated. The LE4 mechanism is understood from a mechanistic study in terms of three etch variables: direct current (DC) bias, gas composition, and sample temperature. For this paper, the effects of DC bias (electron energy) and gas composition (CH₄ concentration) are summarized qualitatively, followed by quantitative evidence. Etch rate, the amount of polymer, surface stoichiometry, and surface roughness have specific relations with each etch variable under competition between pure LE4 and polymer deposition.     

The relationship between the matched-filter operator and the targetsignature space-orthogonal projection classifier

An operator called the target signature space-orthogonal projection classifier (TSC) was recently introduced. The author shows that the TSC is actually a scaling of the familiar matched-filter operator. It is also proved that scaling the matched-filter operator does not alter its receiver operating characteristic (ROC) curve. Therefore, the TSC has the same performance as the matched-filter operator but requires more computations     

Trust model for certificate revocation in ad hoc networks

In this paper we propose a distributed trust model for certificate revocation in ad hoc networks. The proposed model allows trust to be built over time as the number of interactions between nodes increase. Furthermore, trust in a node is defined not only in terms of its potential for maliciousness, but also in terms of the quality of the service it provides. Trust in nodes where there is little or no history of interactions is determined by recommendations from other nodes. If the nodes in the network are selfish, trust is obtained by an exchange of portfolios. Bayesian networks form the underlying basis for this model.     

Dependence of the linewidth enhancement factor on the number of compressively strained quantum well in lasers

We have systematically studied the well number dependence of the linewidth enhancement factor in strained quantum-well (QW) lasers and have demonstrated experimentally that the linewidth enhancement factor can be reduced from /spl sim/9.4 to /spl sim/2.0 by increasing the number of compressively strained QW's from 2 to 8. This behavior is primarily due to an increase in the differential gain with the number of QW's.     

Automated feedback control of body temperature for small animalstudies with MR microscopy

A temperature control system consisting of a thermistor, signal processor, and computer algorithm was developed for magnetic resonance (MR) microscopy of small live animals. With control of body temperature within ±0.2°C of the set point, heart rate is stabilized and, in turn, repetition time (TR) during cardiac-gated studies is less variable. Thus, image quality and resolution are improved     

Genetic algorithms in engineering electromagnetics

This paper presents a tutorial and overview of genetic algorithms for electromagnetic optimization. Genetic-algorithm (GA) optimizers are robust, stochastic search methods modeled on the concepts of natural selection and evolution. The relationship between traditional optimization techniques and the GA is discussed. Step-by-step implementation aspects of the GA are detailed, through an example with the objective of providing useful guidelines for the potential user. Extensive use is made of sidebars and graphical presentation to facilitate understanding. The tutorial is followed by a discussion of several electromagnetic applications in which the GA has proven useful. The applications discussed include the design of lightweight, broadband microwave absorbers, the reduction of array sidelobes in thinned arrays, the design of shaped-beam antenna arrays, the extraction of natural resonance modes of radar targets from backscattered response data, and the design of broadband patch antennas. Genetic-algorithm optimization is shown to be suitable for optimizing a broad class of problems of interest to the electromagnetic community. A comprehensive list of key references, organized by application category, is also provided     

Solder joint reliability of a polymer reinforced wafer level package

Wafer level packages (WLPs) have demonstrated a very clear cost-advantage vs traditional wire-bond technologies, especially for small components that have a high number of dice and I/O per wafer. Ultra CSP^® is a WLP developed by the Kulicke & Soffa Flip Chip Division (formally Flip Chip Technologies). Typical products utilizing the Ultra chip scale package (CSP) have 5×5 or less area arrays at 0.5 mm pitch. This relatively small array has been limited by the inherent solder joint reliability of WLPs. A much larger subset of higher I/O IC’s could benefit from WLPs provided that standard reliability requirements are achieved without the use of underfill.A new polymer reinforcement technology, “Polymer Collar WLP™”, has been developed by K&S Flip Chip Division. Polymer Collar WLP utilizes a polymer reinforcement structure surrounding the solder joint and it has demonstrated more than 50% increase in solder joint life in thermal cycling tests. The most attractive feature of the Polymer Collar WLP process is its simplicity. A simple replacement of the standard solder flux with Polymer Collar material during the solder attach process is all that is required. This simplicity makes Polymer Collar the most cost-effective solution for adding a polymer reinforcement structure to the solder joint. Other methods in use today require additional complex and costly manufacturing steps.This Polymer Collar WLP is expected to widen the WLP market to include larger arrays where the Ultra CSP did not have suitable solder joint reliability.